Jack Straw said anonymity orders were only in force on Jon Venables, Robert Thompson, Mary Bell and Maxine Carr. Photograph: Dan Kitwood/Getty Images

The justice secretary, Jack Straw, today launched a robust defence of giving a new identity to criminals such as Jon Venables when they face the serious possibility of being killed or injured on their release.

"We do not have capital punishment in this country," Straw told MPs. "We did not have rule by lynch mob even when we had capital punishment.

"So there will come a time that there is a high risk when they are released, however grave the offence they have committed, that they face a serious prospect of being maimed or killed."

The justice secretary said such cases were very rare, and such anonymity orders were currently in force only on Venables, Robert Thompson, Mary Bell and Maxine Carr.

Straw said the orders could only be granted when it was judged that the "physical safety, indeed the life of somebody being released, could only be preserved if they are given a new identity".

He added that, despite widespread media reporting of the Venables case over the past 10 days, he believed the original anonymity order issued on his release in 2001 was intact.

"Despite the coverage, the injunction has still held and his current identity has not been compromised," he said.

He placed on the record that the director of public prosecutions had, on Friday, sought a separate injunction to prevent further extensive reporting of the case, including a Sun claim that the new offence possibly committed by Venables was of a serious sexual nature.

"But the learned judge decided not to grant the injunction," he said.

Straw, giving evidence to the justice select committee, resisted becoming drawn into a discussion about whether Venables could now face a fair trial.

However, he defended some of the media's actions, saying there was no regulation of what could be published before somebody was charged.

"The British press do test the boundaries, but once they know where the boundary is they do not go beyond it," he told the committee.

A psychiatric evaluation of Venables, carried out before his release from prison, concluded that he posed a "trivial" risk to the public and the likelihood of him reoffending was "so negligible as to not amount to a serious consideration". Excerpts appear in today's Times.

The document, prepared by a psychiatrist in 2000, also noted that Venables had made "exceptional psychological progress" and had come to terms with his part in the murder of James Bulger in 1993.

"The Jon Venables of today is a very different person to the Jon Venables aged 10," it said.

"It has been a very important part of his rehabilitation so far that he has come to terms in a wholly realistic way with the awfulness of his behaviour."

It emerged last week that Venables – who was given a new identity and released on licence in 2001 – had been recalled to prison following "extremely serious allegations".

Media reports over the weekend suggested that Venables, now 27, had been returned to jail in connection with child pornography offences.

It has also been suggested in the press that he has become mentally fragile, has been known to drink heavily and use drugs and has revealed his true identity to others.

Although the psychiatric report estimated that the chances of Venables being rehabilitated were "exceptionally high", it stressed that his progress depended on him being able to maintain his anonymity and continuing to receive the "appropriate support and guidance".

It also recommended that he be released from juvenile custody rather than placed in the prison system, where exposure to drug-taking and criminals would prove a "very major setback".